"Success is not final, failure is not fatal: it is the courage to continue that counts."
-Winston Churchill
THE DAILY ASTRONOMER
Thirty seven million light years from Earth one finds the beguilingly beautiful Whirlpool Galaxy. Here one can behold a nearly perfect example of a pure spiral galaxy, in which spiral arms curl away from a spherical center so as to lend the entire structure both a vertical and horizontal symmetry. Astronomers believe that the galaxy's current symmetry is a result of its interaction with it companion galaxy, NGC 5195. Were one to observe our own beloved Milky Way from a distance, one would note that the center is barred, not spherical.) Though it contains more than 100 billion stars, the Whirlpool Galaxy is only about 45,000 light years in diameter, less than half the estimated size of the Milky Way. This size is derived directly from the galaxy's angular dimensions and distance, recently measured at 23 million light years.
The Whirlpool Galaxy, or M51, is a beautiful spiral galaxy about 23 million light years from our solar system. We observe the Whirlpool and its companion NGC5195, a smaller galaxy that will soon become incorporated into M51. (Image: National Optical Astronomy Observatory)
When Charles Messier first observed this galaxy in 1773, he discerned very few features and actually described it as a faint nebula devoid of stars. However, in 1845, astronomer Lord Rosse (1800-1867) discerned its spiral structure. It was the first instance in which such spirals were observed in nebula. However, these nebulae were still then believed to have been intergalactic objects. Only in the early twentieth century did Edwin Hubble establish that many of the objects once perceived to have been inside the Milky Way were actually far outside of it.
We now know that the Universe harbors an abundance of galaxies, the population of which might even exceed the number of stars within our own Milky Way. While we cannot see our home galaxy from an external viewpoint, we can observe other galaxies and from observations of their structures infer the design of the Milky Way. The Whirlpool provides us with a very nice, though not precisely accurate, reflection of our own island Universe.
*During the DA school year that begins on September 1, 2016 and ends August 4, 2017, we intend to visit every single Messier, as 2017 will mark the 200th anniversary of Charles Messier's death.